Radiosynthesis, structural identification and in vitro tissue binding study of [18F]FNA-S-ACooP, a novel radiopeptide for targeted PET imaging of fatty acid binding protein 3

Pyry Dillemuth; Tuomas Karskela; Abiodun Ayo; Jesse Ponkamo; Jonne Kunnas; Johan Rajander; Olli Tynninen; Anne Roivainen; Pirjo Laakkonen; Anu J Airaksinen; Xiang-Guo Li

doi:10.1186/s41181-024-00245-3

Radiosynthesis, structural identification and in vitro tissue binding study of [¹⁸F]FNA-S-ACooP, a novel radiopeptide for targeted PET imaging of fatty acid binding protein 3

EJNMMI Radiopharm Chem. 2024 Feb 23;9(1):16. doi: 10.1186/s41181-024-00245-3.

Authors

Pyry Dillemuth^#¹, Tuomas Karskela^#¹, Abiodun Ayo², Jesse Ponkamo¹, Jonne Kunnas^{1

3}, Johan Rajander⁴, Olli Tynninen⁵, Anne Roivainen^{6

7

8}, Pirjo Laakkonen^{2

9

10}, Anu J Airaksinen¹, Xiang-Guo Li^{11

12

13}

Affiliations

¹ Turku PET Centre and Department of Chemistry, University of Turku, Turku, Finland.
² Translational Cancer Medicine Research Program, Faculty of Medicine, University of Helsinki, Helsinki, Finland.
³ Pharmaceutical Sciences Laboratory, Faculty of Sciences and Engineering, Åbo Akademi University, Turku, Finland.
⁴ Accelerator Laboratory, Åbo Akademi University, Turku, Finland.
⁵ Department of Pathology, Helsinki University Hospital and University of Helsinki, Helsinki, Finland.
⁶ Turku PET Centre, University of Turku and Turku University Hospital, Kiinamyllynkatu 4-8, 20520, Turku, Finland.
⁷ Turku Center for Disease Modeling, University of Turku, Turku, Finland.
⁸ InFLAMES Research Flagship, University of Turku, Turku, Finland.
⁹ Laboratory Animal Centre, HiLIFE University of Helsinki, Helsinki, Finland.
¹⁰ iCAN Flagship Program, University of Helsinki, Helsinki, Finland.
¹¹ Turku PET Centre and Department of Chemistry, University of Turku, Turku, Finland. xiali@utu.fi.
¹² Turku PET Centre, University of Turku and Turku University Hospital, Kiinamyllynkatu 4-8, 20520, Turku, Finland. xiali@utu.fi.
¹³ InFLAMES Research Flagship, University of Turku, Turku, Finland. xiali@utu.fi.

^# Contributed equally.

Abstract

Background: Fatty acid binding protein 3 (FABP3) is a target with clinical relevance and the peptide ligand ACooP has been identified for FABP3 targeting. ACooP is a linear decapeptide containing a free amino and thiol group, which provides opportunities for conjugation. This work is to develop methods for radiolabeling of ACooP with fluorine-18 (¹⁸F) for positron emission tomography (PET) applications, and evaluate the binding of the radiolabeled ACooP in human tumor tissue sections with high FABP3 expression.

Results: The prosthetic compound 6-[¹⁸F]fluoronicotinic acid 4-nitrophenyl ester was conveniently prepared with an on-resin ¹⁸F-fluorination in 29.9% radiochemical yield and 96.6% radiochemical purity. Interestingly, 6-[¹⁸F]fluoronicotinic acid 4-nitrophenyl ester conjugated to ACooP exclusively by S-acylation instead of the expected N-acylation, and the chemical identity of the product [¹⁸F]FNA-S-ACooP was confirmed. In the in vitro binding experiments, [¹⁸F]FNA-S-ACooP exhibited heterogeneous and high focal binding in malignant tissue sections, where we also observed abundant FABP3 positivity by immunofluorescence staining. Blocking study further confirmed the [¹⁸F]FNA-S-ACooP binding specificity.

Conclusions: FABP3 targeted ACooP peptide was successfully radiolabeled by S-acylation using 6-[¹⁸F]fluoronicotinic acid 4-nitrophenyl ester as the prosthetic compound. The tissue binding and blocking studies together with anti-FABP3 immunostaining confirmed [¹⁸F]FNA-S-ACooP binding specificity. Further preclinical studies of [¹⁸F]FNA-S-ACooP are warranted.

Keywords: ACooP; Autoradiography; Fatty acid binding protein 3; Fluorine-18; PET; Peptide; Peptide radiolabeling; S-acylation.

Grants and funding

Grant 2021/Syöpäsäätiö